This invention relates to a high-temperature, water-based lubricant and, more particularly, to a water-based graphite suspension useful in metal and mineral forming applications and a continuous process for making the same.
Many metal-forming operations are performed at high temperature using dies, molds and the like. In such operations, lubricants and/or release agents are often used to reduce wear on the dies or molds and to prevent-the resulting metal products from sticking to the dies or molds.
For example, a fluidized iron ore reduction (FIOR) processing plant includes a hot briquetting assembly in which direct reduced iron (DRI) briquettes are formed using iron ore fines as a feed stock. Such a process is described in U.S. Pat. No. 5,082,251 to Whipp, which is herein incorporated by reference. The briquettes are resistant to oxidation during storage and shipping and can be easily handled and charged in steel-making operations. In the briquetting process, reduced iron ore fines, lumps, or pellets are typically metered from a storage drum into a briquetting machine, such as those generally described in U.S. Pat. No. 3,988,095 to Mersh et al. and U.K. Patent No. 1,272,617, both of which are incorporated by reference.
In a briquetting machine, the material to be briquetted is drawn in by rolls rotating in opposite directions and pressed into briquettes at the nip between the pair of rolls by means of briquette-shape molds or dies embedded in the rolls. The iron fines, lumps, or pellets enter a feed drum on the top of the briquetting machine and are forced between the two counter-rotating rolls by a feed screw. The rolls are equipped with briquette-shaped molds which compress the fines into briquettes. The compaction is achieved by a combination of the high pressure between the rolls and the high temperature of the iron feed (approximately 900xc2x0 C.), which makes them more compressible. Roll temperatures range typically between approximately 200xc2x0 to 450xc2x0 C.
Pressure is maintained by means of hydraulic cylinders that exert force against one of the two rollers, one roller being fixed and the other being allowed to move in order to prevent breakage should a piece of metal pass through the machine. The briquettes leave the machine in a web and then are separated into individual briquettes. The briquettes may then be quenched in a water-filled tank and discharged onto a conveyor where the moisture is driven off by the heat remaining in the briquettes.
In the past, dry powdered graphite has been used as a release agent on the briquette rolls used for the DRI hot briquetting. However, the dry graphite has not proved satisfactory in that it does not consistently and uniformly stick to the rolls, resulting in inefficient application of the graphite and high loss of the graphite during the application, and a concomitant graphite dust control problem. Further, the dry graphite is also relatively abrasive, thus resulting in higher wear on the rolls than is desired.
Accordingly, it is an object of this invention to provide a metal working lubricant and release agent that will both minimize wear on the forming rolls and facilitate the release of the formed metal product.
It is a further object to provide such a lubricant that can be efficiently applied to the rolls.
It is a still further object to provide a continuous process for making such a lubricant.
These objects, as well as others which will become apparent upon reference to the following detailed description are accomplished by a high-temperature lubricant comprising a water-base and minor effective amounts of borate, dextrin, graphite, xanthan gum, and an organic preservative. Additionally, a powder for preparing a water-based, high-temperature lubricant is disclosed which comprises graphite and minor effective amounts of borate, dextrin, and xanthan gum. Ranges for the components and preferred embodiments are disclosed for both the liquid lubricant and the powder precursor, as well as processes for making the lubricant.